Semipermeable membranes may be used for a wide variety of separations involving liquid-liquid separations, liquid-liquid solid separations and gas-gas separations. The membranes which are employed for these purposes usually comprise various organic polymers or mixtures of organic polymers either alone or supported on a porous backing material. For example, semipermeable membranes which are used in desalination processes can comprise cellulose acetate polymers composited on a porous support which acts as a backing for the membrane, thin film composite membranes comprising polymeric compounds such as polyethyleneimine, epiamine, polyethylene, polypropylene films also composited on a porous support such as a polysulfone member, etc. Likewise, gaseous separation membranes may comprise polymeric membranes of cellulose nitrate or cellulose acetate support membranes having a polymer such as dimethylsilicone and styrene, composited thereon, as well as thin film membranes such as polymethylpentene polymers. In addition to these membranes other permselective membranes such as heteropoly acids may be employed for separating gases such as hydrogen from mixtures of gases in a gaseous stream.
Some prior patents have shown certain polymeric compositions which are useable in various processes. For example, U.S. Pat. No. 4,071,454 discloses a hollow fiber which is useful for dialysis. However, a dialysis membrane which comprises a plurality of poly(vinyl alcohol) fibers is substantially different from the polymer blends of the present invention in which the latter may be used for a gas-separation. The fiber membranes which have been disclosed in this patent cannot and will not separate a gas inasmuch as they are utilized to physically absorb a whole molecule, that is, the undissociated molecule in the polymer, and subsequently moving said whole molecule through the polymer under the influence of an osmotic pressure gradient. In this respect, the polymer membrane is very similar in nature to a desalination membrane. In like manner, U.S. Pat. No. 4,264,676 discloses superfine fibers of the poly(vinyl alcohol) type which are prepared by baking these superfine fibers in the presence of a dehydration catalyst which may comprise ammonium polyphosphate, phosphoric acid, ammonium phosphate salts and hydrogen chloride. However, the presence of these dehydration catalysts does not provide a membrane of the type of the present invention but is present in the process to cross-link the poly(vinyl alcohol). This occurs through the phosphate ester with the elimination of water.
As will hereinafter be shown in greater detail, the thin film polymer blend membrane of the present invention will be used in a gas separation process. The polymeric material will transport an ion such as a proton through the membrane in a charge transport reaction. In order to ultimately transport a molecule of hydrogen from one side of this membrane to the other, two protons must be formed. The protons are formed by dissociation of molecular hydrogen on a suitable electrode and the transfer of the resulting protons through the membrane and the corresponding electrons through an external circuit. The membranes which were taught in the two previously mentioned patents do not dissociate the molecule but merely provide a means of transporting the nondissociated molecules through the membrane. In other words, the membranes of the patents are moving individual ions from one side to another through the membrane where the ions and electrons, which are supplied by an external circuit, are recombined, on a suitable catalyst, to form molecular hydrogen.
In a majority of cases in prior work, an admixture of an organic compound, especially in a polymeric state, with an inorganic compound, results in a phase separation due to the fact that the two systems are immiscible in nature. However, we have now discovered that a thin film macroscopically homogeneous polymer blended membrane may be fabricated by admixing a phosphoric acid or sulfuric acid with an organic polymer which is at least partially compatible with said acid to form a polymer blended composition of matter which may be utilized as a membrane in a gas-separation process. It was totally unexpected that a thin film membrane could be cast from such blends to provide a membrane which would be highly conductive to protons and therefore find a use in separations involving generation of a proton as in the case of hydrogen.